The contract for the 100,000 barrel per day refinery is said to be worth around $300m, according to Reuters calculations.
Klesch Group has acquired Heide refinery from Royal Dutch Shell in 2010, which has been supplied with crude from a German oilfield Mittelplate and North Sea.
The refinery produces middle distillates such as diesel and heating oil for the local markets of Germany.
Klesch group head Gary Klesch said Barclays has secured business, which was previously done by Glencore Xstrata.
Barclays commodities head Mike Bagguley said, "On financing, we have started to get a critical mass. People know that we are capable of executing these deals."
The latest deal is the third one for Barclays, while it made other two agreements with Hawaiian refinery and British Stanlow refinery.
